The validating machine can either be right by the door in the newer buses or right around the corner at the top of the aisle if you get on in the front of the bus or right to your right as you enter from the back of the bus. Most older buses have 3 doors, you can get in from the front one and back one, and the middle one if for getting off.
The newer buses only have 2 doors, you have to get on at the front of the bus and use the second middle doors to get off.
The machines print/stamp date and time on the ticket and you have 90 minutes from that time for the ticket to be valid, you can get on and off buses while you still have time on that ticket.
Hope this is useful to anyone else with similar questions!